Explicitly set @finish_block, and don't use prep_finalizer to set a finalizer on the Statement.
DEALLOCATE statements during @finish_block.

This plugs a long-standing memory leak!
Finish #execute calls within transaction methods.  (Plugs memory leak.)
Revert "DEALLOCATE statements during @finish_block."

This reverts commit 80f0fe113d06aec661ae39c869984072b743bc91.
Suppress PostgreSQL NOTICE messages during testing.
DEALLOCATE statements during @finish_block.

This plugs a long-standing memory leak!
disconnect: We need to call super before closing our @pg_conn, because the statement finalizers (now) use the connection.